Long-term flexural strengths of resin-modified glass-ionomer cements

The use of resin-modified glass-ionomer cements (RMGICs) in restorative dentistry has expanded since their introduction about seven years ago. These materials have been shown to possess superior initial mechanical properties to those of the conventional glass-ionomer cements. However, studies on the strength of RMGICs as a function of storage time are limited. This in vitro study investigated the effects of long-term storage of RMGICs in two storage media, distilled water and artificial saliva, at 37°C on their four-point and bi-axial flexural stengths for a period up to 1 yr. All materials, except Fuji Lining LC, were weak at 5 min after light exposure but reached the maximum strengths within 7 d. Subsequently, there was a small decline in strength. Generally, the specimens aged in distilled water and artificial saliva had similar strength values. The bi-axial strengths of RMGICs were significantly greater than those obtained from the four-point flexure tests by a factor of approximately three. More variations in strengths of RMGICs with time were also observed from the four-point flexure test than from the bi-axial flexure test.